Light image forming materials of this kind have been conventionally used in many photographic applications as a so-called free radical photograph in which a sensitive area is visualized by exposure of an image.
Particularly effective techniques for free radical photography are methods where various leuco dyes are developed to the corresponding colored dyes by oxidation with photo-oxidizing agents as described, for example, in Photo. Sci. Eng., 5, 98-103 (1961), JP-B No. 43-29407 (the term "JP-B" as used herein means an "examined Japanese patent publication"), JP-A No. 55-55335 (corresponding to U.S. Pat. No. 4,271,251), JP-A No. 57-60329 (corresponding to U.S. Pat. No. 4,298,678) and JP-A No. 62-66254 (corresponding to U.S. Pat. No. 4,622,286) (the term "JP-A" as used herein means an "unexamined published Japanese patent application").
However, these light image forming materials are sensitive to light so that when they are exposed to general indoor light, sunlight or white light, colors are formed even after a dye image is formed by exposure. Hence, there is a difficulty in handling such light image forming materials.
In order to retain the image once the image has formed, color development in areas not irradiated during exposure must be prevented from occurring. For example, it is known to preserve the original image by applying a solution of a reducing agent such as a free radical-capturing, substance (e.g., hydroquinone) to a material having an image formed thereon by means of spraying or impregnation. However, this method requires complicated working and operating conditions since it is a wet process, though this method is advantageous in the preservation and fixing of the original image. There are commercially available materials such as Dylux.RTM. (tradename for a product of du Pont) having the excellent property that an image is formed by UV light and fixed by the activation of a photo-reducing substance with visible light, that is, they can be processed simply by light. However, when a device is exclusively used during the processing period by using light twice in this process, the replacement of spectral filters, etc. must be conducted so that there is a disadvantage that processing speed is unsatisfactory. Further, the above-mentioned JP-B No. 43-29407 discloses that thermal fixing is carried out after the exposure of an image either by incorporating a reducing thermal fixing agent together with a leuco dye and a photo-oxidizing agent in a binder solution, or by overcoating a photosensitive layer with the thermal fixing agent. However, this method has the disadvantage that sensitivity is deteriorated with the passage of time, since the light sensitive parts (the leuco dye and the photo-oxidizing agent) are present with the fixing agent in close proximity to each other.
These light image forming materials comprising the leuco dyes and the photo-oxidizing agents are uniformly dissolved in organic solvents and applied (e.g., by coating, immersion, casting, etc.) to supports such as paper and synthetic resin films. The solvents are evaporated by drying. Accordingly, explosion-proofing precautions for the manufacturing plants thereof due to the use of the volatile organic solvents are required. Thus, these processes are disadvantageous in safety and cost.